Radio control system



March 29, 1949. E. s.I PURINGTON RADIO CONTROL SYSTEM 'Filed May 18,1944 4 Sheets-Sheer,v l

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March 29, 1949. E. s. PuRlNGToN RADIO CONTROL SYSTEM I '4 sheets-sheet'2 Filed May 18, '1944 TON.

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Filed May 18, 1944 `March 29, 1949. l E. s, PURiNGToN 2,465,925

RADIO CONTRGL SYS TEM Filed May 18, 1944 4 Sheets-Sheet 4 l-T 220 n/ d.`ll

osclLLAToR INVENTOR ELLISON $.'PURINGTON.

Patented Mar. 29, 1949 UNITED STATES PATENT FFICE aADlO CoN'rRoL sYs'rEMEllison S. Purington, Gloucester, Mass.,fassignor, by mesne assignments,to Radio Corporation of America, New Yoik, N. Y., .a corporation ofApplication May 418. 1944, Serial No. 536,104

(Cl. 2,5 T17) 20 Claims. 1

This invention relates to a radio control system suitable for use inultra-high frequency channels and has for an object to provide `a systemof the above type adapted forradio dynamic control or for communicationpurposes, which is highly selective and which has characteristics suchvthat it is free to a high degree from interference.

Another object is to provide a system of the above type having novelandimproved details of construction and features of operation.

Various other objects and advantageswill be apparent as the nature ofthe invention is Vmore fully disclosed. s

The present system utilizes two channels in the ultra-high frequencyrange, suchas inthe range of Ll0() to 1000 megacycles, and provides forthe transmission of short, timed pulses on the two channels which may bevaried as to sequence `in accordance with the desired control or signal.The system utilizes a pulse transmitter which is capable of transmittingshort pulses'of comparatively high power.

A radiant energy pulse is sent `from the transmitter to the receiver onone channel followed by a radiant energy pulse on the @they akanne1..There is a frequency separationbetween'the twg channels on whichenergies necessary for operation are sent, and thereis a timeseparationV between the arrival of the two venergies at the re ceiver.The freedom from interference depends largely upon the ramountoifrequency separation of the channels and upon the amount of timeseparation of the energies on `the channels. .A most important factorfis theuse of transmitter energies in the form of vshort dots 4or pulseswith very high peak rradiant power,and with relatively long intervalsbetweenthe pulses,

By the combination of pulsetype transmission, two'radiant energychannels and dilerent times of transmission of the energies onthe. twochannels, an extremely high degree of security is provided.

In the present system the pulses may be from 1.0 to 50 microseconds inlength. The time interval between the pulses is several times thelengtnof the pulses themselves, for example, about 5 to 20 times the length ofthepulses and successive pairs of pulses are separated bya space havinga duration several times the interval 'between the pulses themselves,for eXample,20 to 100 times said time interval.

The control may be` responsive to the receipt o f a single pair ofpulses. Hence .thepOmplete transmission may be of extremelyshortduration, which renders its interception and interference entremelydfult- VHoweveluthe transmissions-may 'pulse from the pulse transmitter.

extend over a plurality of pairs of pulses iffie-Y sred, in whichcasepaccidental interference with one or more of the pairs of pulseswould not affect'lthe control.

While it is Aknown to be physically possibleand practicable to producehigh peak power on a narrow radio band over a short duration of time, itis not practicable to produce alcomparable'high peak powerover both awide radio band and .over a longduration of time, as would be necessary.for successful interference purposes. Ordinary, nonpulse transmitterswould not .be capable of intertering successfully with the vcontrolbecause sutcient power would not be available to produce a response at'the receiver matching in intensity the On the other hand, with `a pulsetransmitter it would be very unlikely thatthe interfering pulse wouldcoincide in time with a control pulse, or vthat its rateof recurrencewould correspond to that of the conltrol pulse as would be required tovproduce interference on succeeding pulses. For high speed telegraphicpurposes, for example, a single ldot or dash might occasionally beobliterated by interference, but for slow speed or radio controlpur-poses, this amount of interference would be entirely negligible.

In accordance with the present invention, a pulse forming circuit isdesigned to form a sfuccessionof pairs of spaced pulses. Thepulses ofeach pairare separated and are used 'individually to modulate radiotransmitting means operating on two different channels, the first pulseof each pair being connected to modulate the transmitter on onechanneland the second pulse of each pairbeing connected to modulate thetransmitter on the other channel. Selective means is provided inthemodulating circuit so that the iirst pulse of each pair may be appliedto either channel at will and the secold pulse may be applied to theother channel. In this way, the pulses are radiated over the twoChannels with a .frequency sequence determined by the selective'meansand with a time interval determined by the original pulse formingcircuit.

In a specific embodiment of the invention the pulsesin the two channelsare received by separate receivers'tuned to the vrespective channels andcontainingtheusual detector circuits to'make the pulses'. available inan output circuit. The outputs ofthe two. receivers are.` connected to atiming comparator which is designed to be responsive Only'whee therulsesere received with a predef termine@ time Species Inoue embodimentthe timing comparator-inf 3 cludes a pulse stretching circuit which isarranged to stretch the pulse from one of the receivers so as to causethe same to overlap in time the pulse from the second receiver when therst pulse is received a predetermined time interval before the secondpulse. The combined effect of the two pulses, when they are thus causedto overlap, is utilized to actuate an output relay circuit. When only asingle pulse is received or when the pulses are not received in propertime sequence to cause the same to overlap in the output circuit of thecomparator no response is produced.

The effect of two overlapping pulses separately applied to the timingcomparator is to produce a single pulse of a duration equal to theamount of time of overlap. This can be applied to a relay Systemoperative on a single pulse, as for example a gaseous type electronicrelay, which however requires a resetdevice such as the use of A. C.plate supply if the control operation is to 4be' repeated. While this issatisfactory for some purposes, it is in general preferable to actuatethe control from the combined effect of a considerable number ofrecurrent pulses giving additional Security by electrical tuning to therecurrence rate.

Instead of utilizing two separate receivers the incoming radiant energymay be received in a single receiver tuned to respond to both channels.The receiver will then include suitable pulse separation means toseparate the pulses received in the respective channels and to applythem to the timing comparator above outlined.

Although the novel features which are believed to be characteristic ofthis invention are pointed out more particularly in the claims appendedhereto, the invention will be better understood by referring to thefollowing description, taken in connection with the accompanyingdrawings in which certain specific embodiments thereof have been setforth for purposes of illustration.

In the drawings:

Fig. 1 is a block diagram indicating the general arrangement of atransmitter and receiver embodying the present invention;

Fig. 2 is a schematic diagram of a pulse forming circuit for use in thesystem of Fig. 1;

Fig. 2a is a series of curves illustrating the operation of the pulseforming circuit;

Fig. 3 is a schematic diagram of a timing comparator -circuit for use inthereceiver of Fig. 1; and

Fig. 4 is a schematic diagram of a pulse receiver utilizing a singleradio receiver tuned to both channels and a pulse separating circuitactuated thereby. In the drawings, the radio transmitter and receivercircuits and the tube circuits are shown only in such detail as isnecessary to an under-- standing of the present invention and it is tobe understood that the circuits are otherwise of' standard and wellknown form and include thevarious potential sources and control elementswhich are well known in the art.

Fig. 1

Referring to Fig. l, the block I represents a pulse forming circuit thedetails of which are shown in Fig. 2 and which is adapted to produce aseries of spaced pairs of pulses a and b and to separate the pulses ofeach pair as indicated in separate circuits terminating at terminals I Iand I2 respectively and having a common ground terminal I 3. The pulse aof each pair of pulses on terminal II is assumed to precede the pulsebon terminal I2 although this sequence may be reversed if desired.

The terminals I I and I2 are connected to poles I4 and I5 respectivelyof a double pole double throw, reversing switch I6 the stationarycontacts of which are connected by lines I'I and I8 respectively, to theinput circuits of radio transmitters and 2l respectively. The radiotransmitters 20 and 2l are preferably of the Shortwave pulse type' andare adapted to radiate carriers on frequencies f1 and f2 amplitudemodulated respectively by the pulses a and b. The transmitters may bedesigned to radiate only when a pulse is received from the pulse formingcircuit I0, so that the energy radiated constitutes a series of spacedpulses occurring first on the frequency f1 and then on the frequency f2for switch position R, or vice versa for switch position L.

The pulses radiated by the transmitters 20 and 2| are received by thereceivers 22 and 23 respectively which are preferably of thesuperheterodyne type terminated with detectors to produce pulses intheir output circuits indicated by the terminals 24, 25, 26 and 2l. Theterminal 24 of the receiver 22 is connected by a line 30 to an inputterminal 3| of a timing comparator 32, the details of which are shown inFig. 3. 'I'he terminal 26 of the receiver 23 is connected by a line 33to an input terminal 34 of the timing comparator 32. The terminals and21 are indicated as connected by a line 35 to ground and.

to a common input terminal 36 of the timing comparator 32.

The timing comparator 32 includes circuits to be described which areselected so that when the pulse on channel .f1 precedes the pulse onchannel f2, a right relay 39 is energized and when the pulse on thechannel f2 precedes the pulse on the channel f1 a left relay 38 isenergized. These relays are provided with armatures 4I and 40respectively which are adapted to close work circuits which mayconstitute selective control for mobile objects such as right and leftsteering controls or a speed control or a suitable signalling circuit,such as an automatic dot-dash receiver.

The arrangement therefore is such that the relays 39 and 38 will beselectively actuated in accordance with the direction of closure of theswitch I6 which controls the sequence of the pulses on the two channels.The switch may, of course, take the form of a push-button, key, or othersuitable device which is readily operated for control or signallingpurposes.

The timing comparator circuit 32 is preferably designed so that nooperation results unless and until both pulses are received and unlessthe pulses are of sufficient duration and length and are spaced withinthe specied time limits. In addition, the system may be designed torespond only when the pulses on the two channels are repeated with arecurrence rate within specied limits. In this way the system is madehighly selective and free from interference.

Fig. 2

Referring to Fig. 2, the pulse forming circuit is shown as comprising amaster oscillator 5U of a type having high stability and designed tooscillate, for example, at 660 cycles per second. The oscillatorincludes a tube 5I and a frequency control circuit 52 together with theusual bias and regulating circuits, all of which are of standardconstruction.

The output circuit of the oscillator 5U includes ate-apt e phase Shifter54. comprising: a condenser and e, resistor 56 connected in series. Theresistor 5,8 isV connected in the input circuit of a vacuum tubeampliiier 89 including an amplifier tube 6I and an output transformer62. The condenser 55 and resistor 56 are preferably of equal numericalimpedance at the frequency of operation so that the voltage across theresistance 56` leads the input voltage to the phase shifter by 45.Hence, the voltage to the amplifier 60 leads the voltage from theoscillator circuit by 45.

The secondary of the transformer 62 is of the push-pull type, the twoends of which are connected to the input grids 5,3, 64 of a pair ofmod.- ulator tubes 65 and 65 respectively. Pulses, formed in the mannerto be described, are applied to the suppressor grids 61 and 68 of thetubes 65 and 55 by a line 69. The plate ycircuit of the tube 65 isconnected by a condenser 10a and a line. 1Q to the output terminal andthe plate circuit of the tube 88 is connected by a condenser 1 |a andaline 1| to the output terminal I2. The two terminals are connectedthrough resistors to a common grounded return line 12 which is connectedto the terminal I3. The tubes 65 and 6.6 are normally biased by theirsuppressor grids to-an inoperative condition and are designed to becapable of passing current only when a voltage pulse is received fromthe line 69.

' The oscillator 5U is also coupled by line 88 through a phase shifter8| consisting of a, resistance 82 and a condenser 83 to the inputcircuit of an amplier tube 84. The phase shifter 8|v is similar to'thephase shifter 54, but in this case the input circuit of the tube 84 isconnected across the condenser of the phase shifter. Hence the voltagesupplied to the tube 84 lags 45 behind tl.e voltage from the oscillatingcircuit. Inasrnuch as the voltage applied to the tube 6,0 leads by 45, a90 phase difference is produced between the voltages applied to thetubes 60 and 84.

The tube 84 feeds, through an output transformer 85, a pair ofrectiflers 86d and 86h having cathodes 86o and 88d' respectivelyconnected to the two ends of the secondary 81 of the transformer andhaving anodes connected together by a line 88 and thence through aresistor 89 and a biasing battery 98 and a return lead` 9| to the centertap of the secondary 81. The biasing bat,- tery 98 is connected todetermine the voltage .values at which current will flow through therectiers due to the voltage impressed by the secondary 81. Rectiedcurrent ows through a tube internally from plate to cathode, thereafter'externally through secondary winding 81 and line 9| to the positive sideof battery 90,y through the battery to the negative side and thencethrough resistor 89 to the plates 89a and 89h of the rectifying tubes.No current flows in resistor 89 except when the cathode of one of therectifiers is negative With, respect to line 9| by an amount exceedingthe voltage value of battery 98.

The positive side of resistor 89 is connected.

to the cathode 92 of a key tube 95, and the negative side of resistor 89is connected to the grid 96 of the key tube 95. At both the positive andthe negative peaks of voltage across secondary 81, the current throughresistor 89 is maximum, so that the grid 9|5` off tube 95 is then highlynegative with respect to the. cathode l92. As the voltage cycleprogresses, the grid 96 of tube 95 comes to cathode potential, therectifying tube vcuts oi dueto battery 90, andthe grid 96 of tube.remains at Cathode potential until the other rectiiying tube becomesconductive thereby returning the grid to a negative value.v In thismanner, the grid of tube 95 is actuated by voltage pulses with a peakvalue which brings the grid of tube 95 to cathode potential and causesit to remain at that potential a short interval of time to formtrapezoidal current pulses occurring at a rate4 of twice thefrequency'of oscillator 58,.

The key tube 95 is shown as a pentode, with the cathode 92 positivelybiased with respect to ground by a battery |01, and with the Screen 93and plate 9.4 positively biased with respect to the cathode bybatteries. m2., lili. The positive side ci battery |83 is connected tothe plate of tube 95 through a, plate. coupling resistor itt. Thesuppressor grid 97. of tube 9.5 is connected by line 98. to a variabletap 99 on resistor lll., one side of which is connected to the negativeand grounded side of battery lill, and the other side oi which isconnected to a liner |48.

In the absence of Voltage across resistors 8.9 and lill), the grid oftube 9.5. is at cathode potential, but nevertheless. no plate currentflows be. cause the cathode is highly positive with respect to thesuppressor. Therefore the control grid pulsesA due to rectification ofvoltage from second.- ary 81 are not repeated to form correspondingplate current pulses. except when the tube 95 is unblocked by acurrentthrcugh resistor |98 which brings the suppressor to the vicinityof cathode potential. A circuit to be described later provides forpulsing resistor |88 recurrently in such a manner that in the embodimentshown the suppressor is. brought to the cathode potential for asufficient time to pass two pulses, from the control grid to plate, thensuppress the passage oi 20 pulses. This isrepeated recurrently in such aWay that for ex,- ample two consecutive pulses out of every twenty twoimpressed on the grid 98 actually produce plate current, leaving aninterval bet-Ween ceIltersr of pairs of pulses 22 times. the intervalbetween centers of the pulses themselves.

Due to the use Vof a high voltage swing from transformer secondary 81,the key tube 95 also operates as a clipper` tube so that only the peaksof the pulses. are repeated into the plate circuit, thereby formingrectangular or slightly trapezoidal shaped output pulses.

The plate 94 of tube 95 is connected through condenser yl I8. to theinput grid |89 of a resistance coupled amplifier stage including pentodeI l, the output of which is coupled through. condenser I4 to line 89.Positive pulses of plate current to tube 95y cause negative pulses ofvoltage to the grid |8901c tube negative pulses of current to the plate|12 of tube` I, and positive pulses of voltage to the line 69r andtherefore to the suppressor grids 67| and 98; of tubes 65 and 68. Thecontrol grids 6.3, 64 ofthe tubes 65 and 88, however, are connected. inpush-pull to the secondary of the transformer 62. Hence one of thesecontrol grids is positive with respect to the. center tap of thetransformer while the other control grid is nega,- tive. When apositivepulse is applied to the suppressor grids 81, 68 from the line 89a pulse is produced in the output circuit of the tube whose control gridis positive at that instant. The pulses supplied to the suppressor gridsare timed by the phase Shifters 54 and 8| to occur on alternate halfcycles of the voltage supplied to the control grid. Hence, one pulsefrom the line e9 is received when the control grid of the tube 65 ispositive and the nextk pulse is received when the control grid of thetube 6,8 is positive, The first lpulse is thus passed through the lead'l0 to the circuit including the output terminal and the next pulse ispassed through the lead 'il to the circuit including the output terminali2, this sequence being repeated whenever a pair or' pulses is appliedfrom line |59. These pulses can be considered as positive pulses ofcurrent towards the plates oi' tubes 65 and 96, and as negative voltagepulses from the output terminals to ground.

Pulse control cincuz't The lead 80 from the oscillator 59 is alsoconnected -to an adjustable phase shifter comprising a pair ofcondensers |2| and a resistor |2.2 connected in series. The resistorI|222 is connected to the input circuit of an amplier tube |23, theoutput circuit of which is connected by means of a tapped resistor |24to the input circuit of an amplifier |25.

The output circuit of the amplifier is connected through a condenser |26to one cathode ||5 and one anode it of a double diode rectier tube |2'|,the other anode lll' of which is connected to a return lead |28 and theother cathode ||8 of which is connected to lead |28 by a con-- denser|29. The double rectier tube |21 and the condensers |26 and |29constitute a portion of a countercircuit which in the embodimentdescribed is designed to operate on a ratio of 11 to 1 Such acountercircuit is well known in the art being described in RCA Review,July 1940, A precision television synchronizing signal generator byBedford and Smith and is accordingly not described herein in furtherdetail. 660 cycle voltage appearing in the output circuit of theamplifier |25 charges the condenser |26 on one half cycle. When theright hand side H6, ||8 of the double rectifier |.2l is conductive thecondenser |26 discharges into the condenser |29 and increases thepotential of its upper plate. On the next half cycle the right hand sideof the double rectier |27 becomes non-conductive so that the chargeremains on the condenser |29, whereas the left hand side |5, of thedouble rectier becomes conductive and allows the charge to leak oir of'7 The multi-vibrator |36 is of standard construction and in the formshown includes a pair of tubes i3? and y|38 having screen and controlgrids which are cross connected, the respective grids being connected toa resistance network including a pair of resistors having variable tapsUli. The arrangement is such that the normal frequency of operation ofthe multi-vibrator |39 in the absence of synchronization will be oneeleventh of B cycles, that is 60 cycles.

This free running value will be controlled to a limited degree by thesetting of the taps |4| on the resistors |40.

The trigger tube |35 is connected to be pulsed when a predeterminedvoltage is applied tothe input circuit thereof by the condenser |29. The

output circuit of the trigger tube is connected to the oscillatingcircuit of the multi-vibrator |36 in such a Way that the multi-vibratorfalls in step with the pulses of the trigger tube over a substantialvariation in setting of the taps |4|.

In the embodiment disclosed the cathode battery |35'a of tube |35 andthe condenser |29 are so chosen so that the condenser will be charged toa suiicient voltage to cause the trigger tube |35 to operate and passcurrent when eleven charges are received from the condenser |26. By thistriggering operation, a synchronizing control voltage is impressed uponthe screen |3`|s of tube |31, due to the current through tube |35. Thiscontrol voltage also causes the plate to cathode branch of tube |31 tobe highly conductive and discharges the condenser to or nearly to groundpotential. Thereupon eleven more cycles of charge on condenser |29 againcause the trigger operation. Hence the multi-vibrator |36 is caused tooperate accurately on a frequency one eleventh of that of oscillator 50,that is at 60 cycles per second. Slight adjustments of phase of themulti-vibrator oscillations can be made by adjusting the capacitance ofthe phase shifting condenser |2|, and by adjustment of the doubleresistor |49.

The multi-vibrator is designed to produce a 60 cycle alternating pulsein the plate circuit of tube |38 with spaced peaks as distinguished froma sine wave. These pulses are applied across a resistance |42 in theinput circuit of a clipper tube |43 which is biased by a battery |43a tooperate only at the peaks of the input pulses. The plate circuit of theclipper tube |43 includes a plate resistance |44 which lowers the platevoltage when plate current flows therein.

The plate |431) of the clipper tube |43 is connected to the inputcircuit of an amplier tube |45 which is normally biased to pass currentand is provided with a plate resistance |45. The plate current of thistube |45, however, is reduced when the grid potential is reduced due toa reduction in plate voltage of the tube |43. This reduction in platecurrent through the plate resistance |45 causes an increase in the platevoltage in the form of a positive voltage pulse which is supplied by acondenser |41 and lead |48 to the resistor |05 above mentioned.

The operation of the multi-vibrator |36 and the bias of the clipper tube|43 are such that the output voltage pulses in the tube |45 are of aduration corresponding to a pair of pulses on the control grid 96 of thetube 95 and are so timed by phase adjustment that the positive bias thussupplied to the suppressor grid 91 of the tube 95 serves to produce asingle pair of pulses in the output circuit of the tube 95. These pulsesare supplied to the suppressor grids 6l, 68 of the tubes 65 and 68 asabove described. With the multi-vibrator |36 operating at 60 cycles, asingle .pair of pulses is released each 60th of a second. Since thepulses themselves are derived from a 660 cycle Wave and are separated byone half a cycle, the spacing of the centers of successive pairs ofpulses is twenty two times the spacing of the individual pulses of eachpair.

Operation of Fig. 2

Ythe tube 95 and serve to unblock the tube 95 during the pulseintervals.

aacute- A 'pulse is applied to the control grid A490 of 'the tube eachtime the voltage in the secondary '81 of the transformer 85 passesthrough zero. The secondary voltage is indicated by the curve E of Fig.2A and the pulses applied to the control grid 93 and repeated as platecurrent are represented at a and b on the curve F. These pulses and bare continuously repeated on the control grid 96 but only appear in theoutput circuit of the tube 95 when they co`incide with a pulse on thesuppressor grid. Hence, only pairs of pulses are produced in the outputcircuit of the tube 35 in dicated by the curve F. M

rThe voltages supplied to the control grid 53; 'l of the respectivetubes 65 and 33 from the master oscillator 50 are represented by thecurves C and D of `Fig. 2a.. It is to be noted that these voltages areboth of 660 cycles frequency but are 180 out of phase due to thepush-pull connection ci the two control grids. When the pulses a and bfrom the output circuit of the tube III are received on the suppressorgrids 61, S8 of the tubes 65 and 63, one or the other of the tubes '35'or 03 is rendered conductive, depending upon which of the tubes isreceiving a positive bias on its control grid at that instantA Y Asillustrated in Fig. 2A, the curve E is displaced 90u with respect to thecurves C and D due to the phase Shifters 54 and 8|. Hence the pulses ofthe curve F Which occur as the curve E crosses the zero axis, coincideWith the peaks of the Waves C and D. In the embodiment illustrated, thefirst pulse a. of the 'curve F occurs during the positive half cycle ofthe curve C which is assumed to be the 'curve of the grid voltage of thetube 55. Hence, the rst pulse of earch paiwill appear in the outputplate circuit kof the tube S5 as indi'- catcd by the curve A or Fig. 2Aand the second pulse of each 'p air will appear in the output platecircuit of the tube BB. `These pulses cause cor'- responding negativevoltage pulses to occur at output terminals 'Iland l2. The phase shifterand resistors' |48 are adjusted to obtain the proper phase relationshipbetween the curve `Gr and the curve F for causing pairs 'of pulses to beproduced, y

Referring novv to Fig'. 1`, the pulses in the output circuit of thepulse forming circuit ,are shown as connected through control switch I6to modulate transmitters 20 and 2 |l which, as previchannels. The pulsea at the terminal I alvvays occurs before thev pulse b at the terminalI2. The control switch ldetermines to which of the transmitters 20 or 2|the first pulse is to be applied. Hence the output Waves of thetransmitters represent a pulse on the channel f1 f'ollpwed by a pulse onthe channel f2 or vice versa, depending upon the position of the switchIt.

Receiving apparatus ously pointed out, are operating on different Thewaves radiated from the transmitters 'zt and 2| of Fig. 1 are shown 'asreceived by the receivers 22 'and 23 which are tuned to the re-vspective Wave frequencies and are of standard construction to make thereceived pulses available in the output circuits of a detector. Thedetectors are 'of a ll'y'uve which will supply 'positive pulsesatterminals4` 24 and 26Hvvith respect to ground terminals 25 and 21. Thesepulses are supplied to the circuitsv including input terminals and 3d ofthe timing comparator 32. The puise at the ternlnall either precedes orlags behind the pulse at the terminal y34 depending upon the sequence of'the transmitted pulses.

10 Theicijrcuitfor the timing comparator 32 is Yshovvn more in detail inFig. 3.

Fig. 3

Referring now to Fig. 3, the terminal 3| is connected by a line '|50 toa resistor |6| in the input circuit of an amplifying triode It/l. Theterminalr34 is connected by a line E33 to a resistor Iti' in the input'circuit of an amplifying triode |55. The return leads from theresistors Ibi and |64 are connected to the terminal 36. The plates u,30| of the triodes |32 and |65 are fed through resistors |66 and |61respectively froin a line |63 connected to a source of plate potentialshown as a battery |10. For sirnplic'ity ci" construction, the triodes|62 and |55 may be' housed in a common envelope, as may other triodes ofthe Fig. 3. They Will be described hoivever for convenience asindependent tubes.

The pulse output of the tube |52 is fed through a condenser I1| to thecontrol grid 302 of a tube |12. The plate 3&3 of tube |12 is connectedthrough a condenser |13 to the control grid 305 of a tube |14. Thecathodes of the tubes |12 and |14 are connected to ground through abiasing battery |15. The plates 303, 3Il5` of the tubes |12 and |14 areconnected to the line |b8 through resistors |13 and |11 respectively.The plate 305 ofthe tube IM is also connected through a resistor |18with the control grid 302 of the tube |12 and through a resistor V|19and a condenser to the control grid `306 of a key tube IBI. The outputcircuit of the amplifier tube |65 is connected by a line |32 through aresistor |83 to the control grid 301 of an amplier tube IM. The plates308, 309 of the tubes IBI and |84 are connected in parallel through aresistance |85 to the line |68.

The tubes |12 and |14 and associated circuits constitute in effect apulse stretching system which operates when energized by a shortnegative pulse on the input grid terminal of tube |12 to produce anegative pulse of longer duration and in the same sense on the outputcircuit of companion tube |14. The output of one tube shown as tube |12is capacity coupled to the input of the other tube |14 as in amulti-Vibrator, but the output of the tube |14 is directly coupled tothe input of the tube |'12 as in an electrical toggle. This system hasone stable equilibrium position in the absence of signals. When thecondition of stable equilibrium is' momentarily upset, as by a pulse ongrid 302 of tube |12 from the plate 300 of tube |32, the system does notinstantaneously return to the equilibrium condition, because of theenergy change in condenser |`|3 during the pulsing. As a result theplate current of output tube |14 continues to change after the pulse ontube |12 has passed. b

In the embodiment shown in the equilibrium condition tube |14 is biasedto below cutoff by battery |15, While tube |12 passes current -due tothe positive voltage on its grid 302 derived fromlbattery |10 throughresistors |11 and |18. A positive pulse applied from terminall 3| toground upon ampliiier |32 causes a negative pulse to be applied from theoutput of tube |62 uponpthe grid 302 of tube |12. In the equilibriumcondition With no current flowing to or from the condenser |13 its lowerplate is at ground potential and its upper plate is at the potential ofthe line |68 diminished by the very heavy drop through resistor |10 tothe plate 303 of the cur- 'ent carrying' tube |12. When now the negativepulse is impressed upon the control grid 302 of tube |12, the platecurrent is momentarily diminished toward or to zero, thereby decreasingthe voltage drop in resistor |19 and increasing the potential on theupper plate of condenser |13. This tends to make the upper plate ofcondenser |13 more positive by a charging current to the condenserfromthe plate 303 of tube |12, and this charging current, represented in thecondenser as a displacement current, causes corresponding current toflow from the lower plate of condenser |13 to ground through the gridresistor 3|0. As a result, both the upper plate and lower plate of thecondenser |13 are raised to a higher potential, and the grid 304 of tube|14 which is connected to the lower plate of condenser |13 is quicklyraised to the potential of the cathode of tube |14 or higher. This inturn increases the current flow to the plate 305 of tube |14, therebylowering its plate potential due to the increased drop through resistor|11. Due to the direct coupling from plate of tube |14 to ground throughresistor |18, the lowering of plate voltage of tube |12 drives its gridnegatively in the same sense as the original pulse. If condenser |13were of infinite capacity, the grid 302 of tube 12 would continue to beheld negative, so that the controlling pulse from tube |62 would befollowed by a permanent holding pulse from tube |14. However due to thecapacity of condenser |13 being nite, the potential across condenser |13changes in accordance with the voltage and resistance in its externalcircuit. With the grid of tube |12 driven negatively beyond cutoff,making tube |12 currentless, condenser |13 is charged to increase itsvoltage toward the limiting value of battery |10. But as it approachesthis value, the charging current diminishes, decreasing the currentthrough the gridto-cathode and grid-to-ground path for tube |14, so thattube |14 commences to draw less current. As a result the potential oftube |12, until now held below cutoi after the control pulse from tube|62 has passed, approaches the cutoff point. When during the charging ofcondenser |13 by a current through resistor |15, the cut-ofi' point oftube |12 is reached, and it commences to pass plate current also throughthe resistor |16, the charging of condenser |13 is checked due to thelowering of voltage applied to the top plate of condenser |13, the gridvoltage of tube |12 drops toward zero and due to the coupling from tube|14 to tube |12 the action of causing tube 12 to pass plate current isaccelerated. With the charging of condenser |13 checked, the operationof the tubes is such as to cause the condenser to discharge t itsequilibrium condition. During this discharge operation, the voltage onthe grid 304 of tube |14 is highly negative beyond cutoil', so thatequilibrium is reached with no further change in plate current of tube|14.

By this action, the negative pulse impressed for a short timeby the tube|62 upon the grid of tube |12 causes an extended positive pulse toappear on the grid of tube |14, and an extended negative pulse to beimpressed from the plate of tube |14 onto the grid 309 of tube |8|.

The alternating current output of the amplifying tube |65 is transmittedthrough line |82 and resistor |83 to the-control grid 301 of triode tube|84. Consequently through the action of tubes |62, |12 and |14, apositive pulse applied to terminal 3| causes a negative pulse with thesame starting time, but of longer duration to be impressed upon theinput of tube |8|. Also by the action of tube |65, a positive pulseapplied to through the resistor |85. The plates 308, 309 are l2 terminal34 causes a corresponding unstretched negative pulse to be impressedupon the input of tube |84. By suitable choice of the resistors and thecondenser |13 associated with pulse stretching tubes |12 and |14, thepulse on tube |8| may be caused to last longer than the time intervalbetween pulses on terminals 3| and 34. Therefore in the event thatterminal 5| is pulsed first and terminal 34 later, within apredetermined time limit established by the action of tubes |12 and |14,overlapping pulses will be impressed on triodes, with the cathodesconnected together and` grounded by a line 3|| and with the plates 308,309 connected together and fed from the line |68 direct coupled throughresistor to the grid 3|2 of a clipper tu-be 9| having its cathode biasedpositive with respect to ground by a battery 3|3 and its plate 3|4 fedfrom the line |68 through a resistor |93. The grid 3| 2 of tube |9| ispositively biased by the direct current flowing through resistors |85and |90 and through the grid resistor 3|5 to ground, but the cathodebattery 3|3 biases the cathode of tube |9| to a much higher potentialthan its grid, so that as a net result, tube |9| is biased considerablybeyond cutoiT so that normally no plate current flows through resistor|93.

Circuit conditions are so adjusted that no current passes throughresistor |93 until the grids of both tubes 8| and |84 are veryconsiderably negative. In the absence of a pulse on tube |8| forexample, cutoff of tube |84 by a negative pulse will cause a change ofplate current through resistor |85, but no effect in resistor |93. Onlywhen the pulses on tubes |8| and |84 are coincidental will there be apulse through resistor |93.

It is possible to utilize the pulse through resistor |93 to trigger oil`a gaseous relay tube, but in the present embodiment, use is made of thefact that the pulses established in resistor |93 are of a recurrentnature.

The plate 3|4 of clipper tube |9| is connected through condenser |94 tothe grid 3| 6 of amplifying triode |95, which in turn is connected toground by a resistor 3| 1 and condenser 3|8 in parallel. The cathode ofthe triode amplifier |95 is grounded by line 3|9 and its plate 320 isconnected to line |68 through a plate resistor 32|.

The plate 320 of tube |95 is coupled through a condenser 322 to theanode 323 of a rectier 200, the cathode of which is connected to groundthrough resistor 20|, bypassed by a condenser 324, and also is connectedto the grid 325 of a relay tube 202. A resistor 326 connected from theanode 323 of rectifier 200 to ground provides a D. C. return path forrectifier 200. The plate 321 of relay tube 202 is connected to thewinding 39 of a relay 328, the other side of which is connected to line|88, and the cathode of relay tube 202 is positively biased by a battery329 so that no plate current will ow unless there is current passingthrough resistor 20| due to action of the rectier 200. The relay 328 isprovided with an armature 4| for closing an external work circuit.

The constants of the circuit associated with amplifier |95 are so chosenthat it selectively integrates and amplies the pulse power derived fromthe plate of clipper tube -|9|. This produces a vcause operation of 'theclipper tube |95.

@interesa 'wave form withhigh proportion ofenergyfcon- 1 tent in thefundamental ratev ofpulsing which is impressed on rectifier B. This waveform is `ireci'iied, and smoothed out by the cathode con- =denser 324 oftube 200, and the D. C. component.'

"With-.in a predetermined time limit, amplifier |62 of Fig. 3 impressesa negative pulse upon pulse v`stretching circuit involving tubes |12,|14 and -resulting in a negative pulse of longer duration impressed uponthe grid 306 of coincidental key tube |8I. The duration of this pulseoverlaps the time interval-'at which a negative pulse is impressed uponcoincidental key tube |84 due to `itl'ie later pulse received from tube|65. By the `coincidental action of tubes |'8l and |84, clipper Vtube|91 is pulsed positively so thata -pulse flows in the plate resistor |93during the interval of overlap. This pulse is broadened, integrated andamplified by "tube |95 and rectied by tube 200 yto cause operation ofthe relay armature 4I.

In the alternative event that switch It of Fig. 1 is thrown for exampleto position L the pulse on terminal v34 precedes that on terminal 3| thecircuit above described will operate to produce pulses in resistor |85which are insufcient to For utilizing the possible control correspondingto terminal 34 being pulsed before terminal 3|, a companion circuit '203is provided. This may be of the same general construction as thatpreviously described, with corresponding parts ldesignated 'by likenumbers but followed by the letter c. However terminal 34 is connectedto drive the grid of tube |6205 'and terminal 3| is connected to `drivethe grid of tube i65a. Therefore the pulse delay circuit 209 responds toa pulse on terminal '34. The output of circuit 259 includes a relay 328mwith armature 4B.

In this manner, the circuit of the timing comparator of Fig, 3 providesfor operation of left relay 32Bit when the switch i6 is closed toposition L which pulses channel f2 before fi and it provides for closureof right 4relay 328 when the switch Il is closed to position R whichpulses channel f1 before fe.

Fig. 4

In the system shown in Fig, 1 two independent ,receivers 22 and 23 areprovided which are tuned respectively to the channels f1 and f2. Fig. 4`shows a circuit for receiving both channels on a single intermediatefrequency type receiver and separating the pulses for application to thetiming comparator. Referring to Fig. 4, the block 2|8) indicates areceiving circuit which is tuned broadly to receive the two channels f1and f2 Asingle frequency local oscillator 2 and a detector 2|'2 areconnected to make the two pulses available as intermediate frequencypulses in an output circuit transformer 2 I5 tuned to both intermediatefrequencies in a well known manner. These pulses are supplied throughthe transformer 2|5 to an amplifier tube 2|S, the output circuit oiwhich is connected `to a well known type of frequency discriminatingcircuit 2|1 which includes coupled inductors 2|8 and 2|9 forming partsof a coupled. circuit system and connected at their les @mid-pointsthrough a condenser 22o. The midpoints of the inductors 2|8 and2|9 arealso connected through a resistor 222 and an inductor 223 to the returnlead 2'24 of the amplifier tube 2|6.

The frequency discriminating circuit 2|'l has characteristics such thatone of the pulses, for example, the intermediate frequency pulsecorresponding to that received on the frequency f1, may be derived fromone end of the inductor 2|9 and applied by a lead 225 to an amplifiertube 226, 'whereas the intermediate frequency pulse corresponding tothat received on the frequency f2 may be derived from the other end ofthe inductor 2 9 and applied by a lead 227 to an amplifier tube 22S. Theoutput Circuits of the amplifier tubes 2256' and 223 are connectedthrough selective intermediate frequency transformers 23|? and 23|respectively to rectiers 232 and 233 respectively. Resistors 234 and235, in circuits with the rectifier's 232 and 233, are connectedrespectively across terminals 24 and 25 and across terminals 26 and 21which correspond to the terminals 24, 25, 26 and 21 of Fig. 1. Thepulses are thus separated 'and made individually available as positivevpulses to the timing comparator.

The operation of this embodiment is similar to that above described'except that only a single receiver is used instead of the two receiversindicated in Fig. 1.

In the embodiment of Fig, 4 a pair of pulses on channels f1 and f2 varereceived and detected in the tuner 2 it and detector 2 I2 and areapplied to the amplifier Zl through a double peaked trans-- former 2|5with transmission peaks corresponding in spacing to the two frequenciesf1 and. f2. These pulses are separated by the frequency discriminatorcircuit 2|'| and are individually amplied in the amplifiers 225 and 22d.The amplifier outputs are rectified by the rectiiiers 232 and 235 toproduce voltage drops in the resistors 234 and 235 in the form ofvoltage pulses corresponding to the received pulses. The pulse receivedon the frequency f1 is thus supplied to the terminals 2li and 25 and thepulse received on the frequency fz is supplied to` the terminals 2G and2l'. These terminals are connected to the timing 'comparator 52 as shownin Fig. 1 wherein their timing is compared and the relays 328 and 3280iare selectively actuated in accordance with the pulse sequence.

It is to be understood that a plurality of channels may be used whichmay be pulsed in selected sequences for a multiple control. A pair ofchannels have been described for purposes of illustration only,

Although certain specific embodiments of the invention have been shownand described in detail, it is to be understood that the invention isnot to be restricted thereto, but is only to be limited in accordancewith the scope of the following claims.

What is claimed is:

l'. A radio transmitting system comprising radio transmitting means topropagate discontinuously pulsed radiant energy substantiallyconcurrently on a plurality of different radio frequency channels, apulse forming circuit to form a series of' discontinuous energy pulseshaving :i predetermined time sequence, means modulating said radiotransmitting means with said pulses to seiectively propagate theindividual pulses of said series on different radio frequency channels,and means controlling the sequence of said pulses on the variouschannels for signalling.

ases-92.5

2. A radio transmitting system comprising radio transmitting means topropagate discontinuously pulsed radiant energy on a pair of differentradio frequency channels, a pulse forming circuit to form a pair ofpulses in predetermined time sequence, means modulating saidtransmitting means with said pulses to propagate one pulse over onechannel and the other pulse over: the other channel in sequence, andmeans con-- trolling said sequence for signalling.

3. A radio transmitting system comprising a pair of radio transmittersconnected to propagate modulated carriers on different radio frequencychannels, a pulse forming circuit connected to form a pair of pulses inpredetermined time sequence, means modulating one of said transmitterswith one of said pulses and means modulat ing the other of saidtransmitters with the other of said pulses, and means selecting thesequence of said pulses for signalling.

4. A pulse forming circuit for forming groups: of pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator and having means converting the impressed` oscillations intoa series of short spaced pulses a plurality of different frequencyoutput circuits each connected to receive different successiveones ofsaid pulses, means normally blocking the transfer of pulse energy to allof said output circuits, a control channel coupled to said oscillator'and having means to convert the impressed oscillations into a series ofpulses spaced by a time interval corresponding to the period of severalof said first pulses and each of a length to overlap at least two ofsaid rst pulses, and means responsive to said last pulses to unblocksaid blocking means and release sequentially a corresponding number ofsaid rst pulses to said output circuits.

5. A pulse forming circuit foi forming groups 1 of pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator, said channel including a pulse forming rectier biased topass current only at the peaks of the applied oscillation to form aseries of short spaced pulses, a plurality of different frequency outputcircuits each connected to receive different successive ones of saidpulses, means normally blocking the transfer of pulse energy to all ofsaid output circuits, a control channel coupled to said oscillator andhaving means to convert the impressed oscillationsinto a series ofpulses spaced by a time interval corresponding to the period of severalof said rst pulses and each of a length to overlap at least two of saidfirst pulses, and means responsive to said last pulses to unblock saidblocking means and release sequentially a corresponding number of saidfirst pulses to each of said output circuits.

6. A pulse forming circuit for forming groups of pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator, said channel including a pulse forming rectier biased topass current only at the peaks of the applied oscillation to form aseries of short spaced pulses, a space discharge device having a controlgrid connected to receive said pulses, a control channel coupled to saidoscillator and having means to convert the impressed oscillations into aseries of pulses spaced by a time interval corresponding to the periodof several of said first pulses and each of a length to overlap at leasttwo of said rst pulses, said space discharge device having a second gridconnected to receive said last pulses and being biased to pass currentonly when pulses are received simultaneously by both of said grids, aplurality of different frequency output circuits fed by said spacedischarge device, and means for elfectively coupling each of said outputcircuits successively to said space discharge device so that successiveones of said first pulses are applied to different ones of said outputcircuits in predetermined sequence.

7. A pulse forming circuit for forming groups A.of pulses, comprising amaster oscillator, a pulse .forming channel coupled to be fed by saidoscillator and having means converting the impressed oscillations into aseries of short spaced pulses, :a plurality of different frequencyoutput circuits each connect-ed to receive different successive ones lofsaid pulses, means normally blocking the trans- .fer of pulse energy tosaid output circuits, a con- :trol channel coupled to said oscillator,said last channel including a pulse forming oscillator operating at afrequency which is a predetermined fraction of the frequency of saidmaster oscillator, coupling means locking said last oscillator into stepwith said first oscillator, pulse forming means converting the energy ofsaid last oscillator into a series of pulses spaced by time :intervalscorresponding to the period of several :off said first pulses and eachof a length to over- ;l'ap at least two of said iirst pulses, and means:responsive to said last pulses to unblock said iolocking means andrelease a corresponding numlber of said first pulses successively todifferent ones of said output circuits.

8. A pulse forming circuit for forming groups of pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator and having means converting the impressed oscillations into aseries of short spaced pulses, a plurality of different frequency outputcircuits each connected to receive successively different ones of saidpulses, means normally blocking the transfer of pulse energy to saidoutput circuits, a control channel coupled to said oscillator, said lastchannel having a counter-circuit connected to produce pulses having afrequency which is a predetermined fraction of the frequency of saidmaster oscillator, a second oscillator connected to :saidcounter-circuit to operate at the frequency .of said last pulses, apulse forming circuit conlnected to convert the oscillations of saidlast oscillator into a series of pulses spaced by a time intervalcorresponding to the period of several of said first pulses and each ofa length to overlap :at least two of said rst pulses, and meansresponsive to said last pulses to unblock said blocking means andrelease successive ones of said first pulses to different ones of eachof said output circuits.

9. A pulse forming circuit for forming groups of pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator and having means converting the impressed oscillations into aseries of short spaced pulses, a plurality-of different frequency outputcircuits each connected to receive successively different ones of saidpulses, means normally blocking the transfer of pulse energy to saidoutput circuits, a control channel coupled to said oscillator, said lastchannel containing a counter-circuit connected to have a pulse frequencycorresponding to a predetermined fraction of the frequency of saidmaster oscillator, a multi-Vibrator connected to operate in step withsaid last pulse frequency, a pulse forming circuit fed by saidmulti-vibrator and connected to convert the oscillations thereof into aseries of pulses spaced by a time interval corresponding to the periodof several of said first pulses and each of a length to overlap at leasttwo of said first pulses, and means responsive to said last pulses tounblock said blocking means and release successive ones of said firstpulses to dierent ones of said output circuits.

10. A pulse forming circuit for forming pairs of pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator and having means to convert the impressed oscillations into aseries of short spaced pulses, a pulse circuit connected to receive saidpulses, means normally blocking the transfer of energy to said pulsecircuit, a control channel coupled to said oscillator and having meansto convert the impressed oscillations into a series of pulses spaced bytime intervals corresponding to the period of several of said iirstpulses and each of a length to overlap at leat tvvo of said firstpulses, means responsive to said last pulses to unblock said blockingmeans and release a pair of said first pulses to said pulse circuit, anoutput circuit fed by said oscillator and having different radiofrequency output channels selective respectively of the positive andnegative half cycles of the impressed oscillations and normally blocked,and means responsive to said pulse circuit to unblock said outputchannels for thereby selectively transmitting thereover the individualpulses of said pair which coincide in time with the positive andnegative half cycles respectively.

11. A pulse forming circuit for forming pairs of pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator and having means to convert the impressed oscillations into aseries of short spaced pulses, a pulse circuit connected to receive saidpulses, means normally blocking the transfer of energy to said pulsecircuit, a control channel coupled to said oscillator and having meansto convert the impressed oscillations into a series of pulses spaced bytime intervals corresponding to the period of several of said firstpulses and each of a length to overlap at least two of said firstpulses, means responsive to said last pulses to unblock said blockingmeans and release a pair of said rst pulses to said pulse circuit, anoutput channel coupled to be fed by said master oscillator and having apair of space discharge devices having input circuits connected inpushpull relationship to be responsive to alternate half cycles of theimpressed oscillations, individual different radio frequency outputcircuits fed by the respective space discharge devices, said devicesbeing normally blocked, and means connecting said pulse circuit tounblock said devices for producing pulses in the respective outputcircuits thereof corresponding to the individual pulses of said pairwhich coincide in time with the positive and negative half cyclesrespectively.

12. A pulse forming circuit for forming pairs of pulses, comprising amaster oscillator, a pulse output channel comprising a pair of normallyblocked space discharge devices having input circuits connected inpush-pull relationship and coupled to be actuated by said oscillator,individual diierent radio frequency output circuits fed by therespective devices, a pulse forming channel coupled to be fed by saidoscillator and having means forming a series of short, spaced pulsescorresponding to the successive half cycles of the impressedoscillations, a normally blocked 18 l space discharge device having aninput circuit 'ied by said last pulses and having an output circuitconnected to unblock said first devices, and a control channel alsocoupled to said oscillator and having a frequency converter to produce aWave having a irequency which is a predetermined fraction of theoscillator frequency, means producing a series of short spaced pulseshaving a frequency corresponding to said last frequency and having alength corresponding to a pair of said first pulses, and means supplyingsaid last pulses to unblock said last device for supplying thereby saidpair oi pulses to unblock said rst devices so as to supply theindividual pulses of said pair alternately to said output circuits.

A pulse forming circuit for forming groups oi' pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator and having means converting the impressed oscillations intoseries of short spaced pulses, a pair of different radio frequencyoutput circuits each connected to receive diierent successive ones ofsaid pulses, means normally blocking the transfer of pulse energy tosaid output circuits, a control channel coupled to said oscillator andhaving means to convert the impressed oscillations into a series ofpulses spaced by a time interval corresponding to the period of severalof said first pulses and each of a length to overlap at least two ofsaid first pulses, phase shifting means to cause said last pulses tooverlap a pair of said first pulses, and means responsive to said lastpulses to unblock said blocking means and release a corresponding numberof said rst pulses successively to said output circuits.

14. A pulse forming circuit for forming pairs of pulses, comprising amaster oscillator, a pulse forming channel coupled to be fed by saidoscillator and having means to convert the impressed oscillations into aseries of short spaced pulses, a pulse circuit connected to receive saidpulses, means normally blocking the transfer of energy to said pulsecircuit, a control channel coupled to said oscillator and having meansto convert the impressed oscillations into a series of pulses spaced bytime intervals corresponding to the period of several of said iirstpulses and each of a length to overlap at least two of said rst pulses,means responsive to said last pulses to unblock said blocking means andrelease a pair of said first pulses to said pulse circuit, an outputcircuit fed by said oscillator and having different radio frequencyoutput channels selective respectively of the positive and negative halfcycles of the impressed oscillations and normally blocked, phaseshifting means to cause said first pulses to coincide with theoscillator half cycles, and means responsive to said pulse circuit tounblock said output channels for thereby selectively transmittingthereover the individual pulses of said pair which coincide in time Withthe positive and negative half cycles respectively.

15. A pulse forming circuit comprising a master oscillator, a pulseforming channel coupled to be fed by said oscillator, said channelincluding a pulse forming rectifier biased to pass current only at thepeaks of the applied oscillation in the form of a series of spacedpulses, a space discharge device having a control grid connected toreceive said pulses, said device normally passing current and beingbiased to cut off in response to said pulses whereby current pulses areproduced in sai-d device when the oscillator voltage passes throughZero, an output circuit fed by said oscillator and having difierentradio frequency outputchannels selective respectively of the positiveand negative half cycles of the impressed oscillation and normallyblocked, phase shifting means to cause said current pulses to coincidewith the positive and negative half cycles in said output channels, andmeans responsive to said current pulses to unblock said output channelsfor thereby selectively transmitting thereover the individual pulseswhich coincide in time with the positive and negative half cyclesrespectively.

16. A pulse forming circuit comprising a master oscillator, a pulseforming channel coupled to be fed by said oscillator, said channelincluding a pulse forming rectier biased to pass current only at thepeaks of the applied oscillation in the form of a series of spacedpulses, a space discharge device having a control grid connected toreceive said pulses, said device normally passing current and beingbiased to cut off in re-I sponse to said pulses whereby current pulsesare produced in said device when the oscillator voltage passes throughzero, and a space discharge device having a control grid connected toreceive said last pulses and biased to pass current only on the peaks ofsaid last pulses to thereby produce short spaced current pulses, anoutput circuit fed by said oscillator and having different radiofrequency output channels selective respectively of the positive andnegative half cyclesh of the impressed oscillations and normallyblocked, phase shifting means to cause said current pulses to coincidewith the positive and negative half cycles in said output channels, andmeans responsive to lsaid current pulses to unblock said output channelsfor thereby selectively transmitting thereover the individual pulseswhich coincide in time with the positive and negative half cyclesrespectively.

17. A pulse forming circuit comprising a mas-- ter oscillator, a pulseforming channel coupled to be fed by said oscillator, said channelincluding a pulse forming rectifier biased to pass current only at thepeaks of the applied oscillations in the form of a series of spacedpulses, a spacev discharge device having a control grid connected toreceive said pulses, a plurality of output circuits fed by said spacedischarge device, and means for feeding said pulses derived from said-device successively to different ones of said output circuits.

18. A pulse forming circuit comprising a master oscillator, a pulseforming channel coupled to be fed by said oscillator having meansclonverting the impressed oscillations into a series of spaced pulses,an output circuit fed by said ilu oscillator and having different radiofrequency output channels selective respectively of the positive andnegative half cycles of the impressed oscillations and normally blocked,and means responsive to said pulses to unblock said output channels forthereby selectively transmitting thereover the individual pulses whichcoincide in time with the positive and negative half cyclesrespectively.

19. A pulse forming circuit comprising a master oscillator, a pulseforming channel coupled to be fed by said oscillator having meansconverting the impressed oscillations into a series of spaced pulses, anoutput channel coupled to be fed by said master oscillator and having apair of space discharge devices having input circuits connected inpush-pull relationship to be responsive to alternate half cycles of theimpressed oscillations, individual different radio frequency outputcircuits fed by the respective space discharge devices, said devicesbeing normally blocked and means connecting said pulse circuit tounblock said devices for producing pulses in the respective outputcircuits thereof corresponding to the individual pulses which coincidein time with the positive and negative half cycles respectively.

20. A pulse transmission system comprising a. source of alternatingcurrent, a pair of diierent radio frequency output channels connected tobe selectively fed by the positive and negative half cycles respectivelyfof said current, a pulse forming circuit coupled to said source andhaving means converting each half cycle into a short pulse, and meansmodulating said output channels With said pulses whereby alternatepulses are transmitted over diiTerent channels.

ELLISON S. PURINGTON.

REFERENCES CITED The following references are of record in the oi thispatent:

UNITED STATES PATENTS Number Name Date 1,805,918 Meissner May 19, 19312,113,011 White Apr. 5, 1938 2,153,179 Fitch Apr. 4, 1939 2,211,942White Aug. 20, 1940 2,235,768 Luck Mar. 18, 1941 2,286,377 Roberts June16, 1942 2,352,634 Hull July 14, 1944 2,357,398 Gray Sept. 5, 19442,405,237 Ruhlig Aug, 6, 1946 2,405,238 Seeley Aug. 6, 1946 2,405,239Seeley Aug. 6, 1946

